Flushing apparatus for reversible hydrostatic drives

ABSTRACT

A FLUSHING DEVICE FOR REVERSIBLE HYDROSTATIC DRIVES OF THE TYPE EMBODYING A FLUSHING PUMP AND A RESPECTIVE FREED VALVE MEANS FOR EACH PRESSURE SIDE OF THE DRIVE. THERE IS FURTHER PROVIDED A FLUSHING VALVE MEANS WHICH IS CONTROLLED BY THE MOMENTARY PREVAILING HIGH PRESSURE. A PRESSURE LIMITING VALVE MEANS WHICH IS CONNECTED AFTER THE FLUSHING VALVE MEANS INCORPORATES A PISTON MEMBER WHICH IS IMPACTED VIA A DIRECT CONNECTION BY THE FLUSHING PUMP MEANS. THIS PISTON MEMBER IS PROVIDED WITH TWO CONTROL EDGE PORTIONS, ONE OF WHICH IS EFFECTIVE WHEN THE SLIDE MEMBER OF THE FLUSHING VALVE MEANS IS IN ITS NULL OR NEUTRAL POSITION AND THE OTHER OF WHICH IS EFFECTIVE WHEN SUCH SLIDE MEMBER HAS ASSUMED AN OPERATING POSITION.

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Feb. 9,'197'1 United States Patent O 3,561,214 FLUSHING APPARATUS FOR REVERSIBLE HYDROSTATIC DRIVES Gerhard Bobst, Oensingen, Switzerland, assignor to Von Roll AG, Gerlafingen, Switzerland, a corporation of Switzerland Filed Apr. 26, 1968, Ser. No. 724,498 'Claims priority, application Switzerland, May 2, 1967, 6,263/ 67 Int. Cl. F16d 31/00 U.S. Cl. 60--53 4 Claims ABSTRACT F THE DISCLOSURE A flushing device for reversible hydrostatic drives of the type embodying a flushing pump and a respective feed valve means for each pressure side of the drive. There is further provided a flushing valve means which is controlled by the momentary prevailing high pressure. A pressure limiting valve means -which is connected after the flushing valve means incorporates a piston member Which is impacted via a direct connection by the flushing pump means. This piston member is provided with two control edge portions, one of which is effective when the slide member of the flushing valve means is in its null or neutral position and the other of which is effective when such slide member has assumed an operating position.

BACKGROUND OF THE INVENTION The present invention relates to an improved flushing or scavaging device for reversible hydrostatic drives and is of the type comprising a flushing or scavaging pump, a respective feed valve means for each pressure side of the drive, a fiushing valve means controlled by the momentarily prevailing high pressure and a pressure limiting valve means.

It is known in the prior lart for fiuid drives which work in a closed fluid circuit to feed oil to the momentary low pressure side by means of a special pump through the agency of a respective check or nonreturn valve. This is undertaken in order to replace any leakage oil losses in the drive, but also for replenishing the circulating oil. In s0 doing, it is possible to remove from the fluid circuit any possible foreign bodies and air inclusons as well as to maintain the oil temperature within the permissible temperature range. The flushing or scavaging operation takes place by means of a valve which is controlled by the pressure at the high pressure side. This valve opens the momentary low pressure side and feeds the quantity of flushing fluid delivered by the pump minus the leakage losses via a low pressure valve back to the reservoir of the flushing or scavaging pump. At this location the fluid is again sucked up by the flushing pump and delivered through the pressure conduit and, if desired, via filter means and heat exchange means through the corresponding check valve which is designated as a feed valve to the low pressure side of the drive. There is thus provided a complete fluid circuit within which there occurs a partial exchange of oil with the drive circuit.

The mentioned flushing valve is operatively connected with a respective connection to both pressure sides of the drive. It is generally constructed in the form of a slide valve, which in both terminal positions closes the momentary pressure side and communicates the low pressure side with the drain or discharge controlled by a pressure limiting valve. In its neutral or central position, that is to say, when the drive does not transmit any power or work, in other words the primary portion of the drive has a zero or null stroke volume, the

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flushing valve closes both connections to` the discharge or considerably throttles them. In both cases this results in a corresponding pressure increase which is limited by the provision of a pressure limiting valve arranged at the flushing or scavaging pump. Thus, two pressure limiting valves are provided at the flushing circuit, of which, however, the one pressure limiting valve at the flushing pump must be adjusted to a higher pressure in order to fulfill the purpose of the flushing circuit than the pressure limiting valve which is arranged after the ushing Valve.

Furthermore, a flushing fluid circuit is known in which a single pressure limiting valve is arranged after the flushing valve. The slide member of the flushing valve is constructed, in this case, as a hollow slide and therefore can be employed as the flow path for the quantity of uid delivered by the flushing pump when the flushing valve is in its central position. In the terminal positions of the slide member this path is blocked or closed, the flushing oil arriving via the relevant feed valve at the low pressure side and ows via the flushing valve and the low pressure valve back to the reservoir.

Notwithstanding the fact that by virtue of this solution the flushing circuit is simplified, still there must be kept in mind that several considerable drawbacks exist. The use of flow paths withinthe slide member requires large dimensioned slide members in order to avoid excessively large pressure losses. However, large slide members require large displacement forces, so that the quick reversibility of the drive is no longer ensured. On the other hand, if such large slide members are once placed into motion, then appropriately dimensioned dampening devices must be provided in order to prevent any damage to the slide member when it stops.

In order to prevent these disadvantages it is necessary to use a light flushing valve and to equip such with effective dampening devices. Only in this m-anner can the flushing or scavaging valve be rendered an operationally reliable part of the hydrostatic drive which is protected against damage due to impact. Therefore, it was necessary to again return to the solution which incorporates two pressure limiting valves, one arranged at the flushing pump and the other after the flushing valve.

SUMMARY OF THE INVENTION Accordingly, it is a primary purpose of the present invention to provide an improved flushing device for the purposes heretofore described which, notwithstanding the use of a light flushing valve, can reliably operate with a single pressure limiting valve.

Another object of the present invention is to provide an improved flushing device for reversible hydrostatic drives which effectively overcomes the aforementioned drawbacks of the prior art structures.

Broadly speaking, the invention is manifested by the features that the piston of the pressure limiting valve which is connected after the flushing valve is impacted via a direct connection by the flushing pump and this piston possesses two control-edge portions, one of which is effective when the slide member of the flushing valve is in its null or neutral position, and the other of which is effective when such slide member has assumed an operating position.

BRIEF DESCRIPTION OF THE DRAWING The invention will be better understood, and objects other than those set forth above, will become apparent, when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawing, wherein:

FIG. 1 illustrates a preferred embodiment of the inventive flushing device, partially shown in section and partially schematically represented in order to improve clarity in illustration;

FIG. 2 is a fragmentary view, partially in section, of details of the flushing slide member and the pressure limiting valve, with the flushing slide member in its null or neutral position; and

FIG. 3 is a cross-sectional view taken through the flushing slide piston depicted in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Describing now the drawing, it will be understood that reference numeral 1 represents an adjustable primary unit which is driven by a non-illustrated prime mover and reference numeral 2 designates the fixed secondary unit of a hydrostatic drive which drives a non-illustrated working machine. The flushing fluid circuit comprises the constant delivery pump 3 which can be driven from the same prime mover as the primary unit 1 or can be separately driven. Further, it comprises both of the feed Valves 4 and 4" which are constructed as nonreturn or check valves. Additionally, the illustrated flushing circuit incorporates the flushing valve means 6 which is connected via the conduits 5 and 5 to the pressure sides and further includes the pressure limiting valve means 8 which is connected after the flushing valve means 6 via the connection means 7. The oil can flow from the pressure limiting valve means 8 via the discharge conduit 9 back into the reservoir 10 which is identical with the reservoir which is located beneath the flushing pump 3. Additionally, there will be recognized a separate conduit 11 by means of which the flushing pump 3 can impact the pressure limiting valve means 8.

The flushing valve means 6 embodies a piston slide member or spool 12 having a longitudinal bore dening a canal 12". Additionally the piston slide member 12 iS provided at its middle region with cut-away or recessed portions 12' (FIG. 3) and at both ends is equipped with a substantially cylindrical projection 13 having a smaller diameter than the middle region of the aforementioned piston slide member 12. Further, it will be seen that in the compartments or chambers 14 and 14l there is located a respective spring member 15 which serves to press the associated throughbored spring plate 16 against the shoulders or projections 17.

The fiushing slide operates in the following manner: In the null or neutral position, as shown in FIG. 2, the pressure in both pressure conduits, and therefore in the conduits 5 and 5" is the same. If the pressure in the upper conduit increases, then, the piston member 12 is displaced into its lower terminal position and opens the lower pressure conduit via the conduit 5 into the connection means or connecting chamber 7.

As a result, the cylindrical projection 13 is displaced into the chamber or compartment 14', as shown in FIG. l, and thus raises the spring 15 and the spring plate 16. In the terminal phase of the movement of the valve member 12 there is formed between the shoulder or projection means 17 and the end face of the piston member 12 a chamber out of which the oil can only flow throttled and thus acts as an effective dampennig device. This dampening operation is additionally supplemented in that the high pressure is transmitted through the longitudinal bore 12 of the piston member 12 to the opposite side and at that location a pressure builds up which almost retains the piston member in equilibrium. Since this build-up of pressure only occurs towards the end of the stroke of the piston member 12, the quick reversibility of the piston member 12 is not prevented. This combination of throttling and pressure dampening is essential for the rapid stopping of the piston member. As soon as the pressure again drops, then the spring member 15 again displaces the piston member into its neutral position and the conduits 5 and 5" are blocked, as shown in FIG. 2.

However, the flushing pump 3 continues to convey fluid medium via the conduit 11 to the underside of the piston 18 provided with a weak spring member 18. The pressure is transmitted through this hollow bored piston 18 via the throttling orifice 19 to the cone valve means 20 which is loaded by a spring 21. If the pressure opens the cone valve means 20 and allows the oil to flow through the channel 20', then owing to the throttle orifice 19 the pressure beneath the cone valve means 20 drops and the piston 18 opens the control edge portion 22 thereof (as shown in FIG. 2) and the flushing oil from conduit 11 can flow back into the reservoir 10. The control edge portion 22" of the piston 18 likewise opens the discharge from connection means 7 to conduit 9, but because of the central or neutral position of the piston member 12 no discharge occurs. This is the position of the apparatus depicted in FIG. 2. On the other hand, if the piston member 12 is located in the terminal position, as shown in FIG. 1, then the discharge takes place at the control edge portion 22.

If the valve opening at the control edge portion 22" is greater than what would correspond to the quantity of fluid delivered by the pump 3, then the pressure in the closed ushing circuit drops. The valve 8 closes to such extent until the discharge from the flushing valve means 6 is throttled by the control edge portion 22. However, in the throttle position of the control edge portion 22 the control edge portion 22 is closed. On the other hand, if the delivered quantity of fluid medium of the pump 3 is greater than the valve opening at the control edge portion 22, then a part of the fluid medium must flow away via such control edge portion 22', since the pressure cannot be greater than that corresponding to the adjustment of the valve means 20. Hence, with the flushing valve means 6 in the position of FIG. l, flushing fluid medium ows either past the control edge portion 22", control edge portion 22 being closed, or else flushing fiuid medium flows away past the control edge portion 22 when the quantity of flushing fluid medium can not completely pass through the opening at the control edge portion 22". On the other hand, in the position of the ushing valve 6 of FIG. 2, the total quantity of Hushing medium flows away via the control edge portion 22. The small quantity of medium flowing away via the precontrol valve 20, in both positions of the flushing valve means 6, need not be taken into account since it is very small.

By virtue of this arrangement there is provided a flushing device which satisfies the highest requirements regarding speed of reversibility, freedom from wear because of extremely effective dampening and sufficiently large channels notwithstanding the smallest piston mass.

It is not necessary that the piston member 12 seals completely in the neutral position, rather a throttled throughflow is also permissible. Nonetheless, in this case the control edge portion 22 is effective since the larger oil stream flows away via the conduit 11, whereas the discharge through the connection means 7 takes place at a lower pressure than the supply or feed pressure.

The combination of throttling and pressure dampening which is possible by virtue of the longitudinal bore 12 provided at the piston member 12, has still the further advantage that, independently of the pressure side of the main fluid circuit, the high pressure can always be removed at the same location, as such is represented in FIG. 1 by the reference numerals HD. This pressure can be, for instance, used to control further hydraulic or hydrodevices.

Instead of the pre-controlled pressure limiting valve which has been shown in the exemplary embodiment, it would also be possible to utilize a direct controlled valve. In this case, then, the flushing pressure in the null-position of the flushing valve is somewhat larger than during the operating position, since the opening of the edges must take place in succession.

While there is shown and described a present preferred embodiment of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the following claims.

Accordingly what is claimed is:

1. In combination with a reversible hydrostatic drive having a momentary high pressure side and low pressure side, a flushing device comprising ushing pump means, a respective feed valve means communicating each pressure side of the hydrostatic drive with said flushing pump, a flushing valve means controlled by the momentary prevailing high pressure of the high pressure side, said ilushing valve means including a flushing slide member, pressure limiting valve means operably connected with said ilushing valve means, said pressure limiting valve means including a piston member and a discharge, means providing a direct connection from said flushing pump means to said pressure limiting valve means so that fluid medium delivered by said ilushing pump means impacts said piston member, said piston member being provided with two control edge portions, one of said control edge portions being eective to establish communication between said ilushing pump means and said discharge of said pressure limiting valve means when said flushing slide member is in its neutral position, and the other of said control edge portions being effective to establish communication between said ushing valve means and said discharge of said pressure limiting valve means when said llushing slide member has assumed an operating position.

2. The combination of claim 1, wherein said pressure limiting valve is constructed as a pre-controlled valve.

3. The combination of claim 1, wherein said ilushing slide member incorporates a piston provided with a substantially cylindrical projection of smaller diameter than the diameter of said piston, said ilushing Valve means incorporating shoulder means, said cylindrical projection cooperating with said shoulder means and an end face of said piston at the end of its stroke in order to provide a throttle dampening means.

4. The combination of claim 1, wherein said ushing slide member incorporates a piston provided with a longitudinal bore.

ROBERT G. NILSON, Primary Examiner 

